The present invention relates generally to implantable pacemakers and particularly to a subcutaneous electrode used to sense, record, and acquire electrocardiographic data and waveform tracings from an implanted pacemaker without the need for or use of surface (skin) electrodes. More particularly, the present invention relates to thin film electrodes placed onto a modified top surface of a feedthrough fitting into an assembly incorporated along and into the peripheral edge of the implantable pacemaker. Each thin film electrode becomes an integral element of a Subcutaneous Electrode Array or SEA that, in turn, detects cardiac depolarizations communicable and displayable by a portable device programmer.
The electrocardiogram (ECG) is commonly used in medicine to determine the status of the electrical conduction system of the human heart. As practiced, an ECG recording device is commonly attached to the patient via ECG leads connected to pads arrayed on the patient""s body so as to achieve a recording that displays the cardiac waveforms in any one of 12 possible vectors.
Since the implantation of the first cardiac pacemaker, implantable medical device technology has advanced with the development of sophisticated, programmable cardiac pacemakers, pacemaker-cardioverter-defibrillator arrhythmia control devices and drug administration devices designed to detect arrhythmias and apply appropriate therapies. The detection and discrimination between various arrhythmic episodes in order to trigger the delivery of an appropriate therapy is of considerable interest. Prescription for implantation and programming of the implanted device are based on the analysis of the PQRST electrocardiogram (ECG) and the electrogram (EGM). The waveforms are usually separated for such analysis into the P-wave and R-wave in systems that are designed to detect the depolarization of the atrium and ventricle respectively. Such systems employ detection of the occurrence of the P-wave and R-wave, analysis of the rate, regularity, and onset of variations in the rate of recurrence of the P-wave and R-wave, the morphology of the P-wave and R-wave and the direction of propagation of the depolarization represented by the P-wave and R-wave in the heart. The detection, analysis and storage of such EGM data within implanted medical devices are well known in the art. Acquisition and use of ECG tracing(s), on the other hand, has generally been limited to the use of an external ECG recording machine attached to the patient via surface electrodes of one sort or another.
The aforementioned ECG systems that utilize detection and analysis of the PQRST complex are all dependent upon the spatial orientation and number of electrodes located on the body or placed near and around the heart to detect the depolarization wave front.
As the functional sophistication and complexity of implantable medical device systems increased over the years, it has become increasingly more important for such systems to include a system for facilitating communication between one implanted device and another implanted device and/or an external device, for example, a programming console, monitoring system, or the like. For diagnostic purposes, it is desirable that the implanted device be able to communicate information regarding the device""s operational status and the patient""s condition to the physician or clinician. State of the art implantable devices are available which can even transmit a digitized electrical signal to display electrical cardiac activity (e.g., an ECG, EGM, or the like) for storage and/or analysis by an external device. The surface ECG, however, has remained the standard diagnostic tool since the very beginning of pacing and remains so today.
To diagnose and measure cardiac events, the cardiologist has several tools from which to choose. Such tools include twelve-lead electrocardiograms, exercise stress electrocardiograms, Holter monitoring, radioisotope imaging, coronary angiography, myocardial biopsy, and blood serum enzyme tests. Of these, the twelve-lead electrocardiogram (ECG) is generally the first procedure used to determine cardiac status prior to implanting a pacing system; thereafter, the physician will normally use an ECG available through the programmer to check the pacemaker""s efficacy after implantation. Such ECG tracings are placed into the patient""s records and used for comparison to more recent tracings. It must be noted, however, that whenever an ECG recording is required (whether through a direct connection to an ECG recording device or to a pacemaker programmer), external electrodes and leads must be used.
Unfortunately, surface electrodes have some serious drawbacks. For example, electrocardiogram analysis performed using existing external or body surface ECG systems can be limited by mechanical problems and poor signal quality. Electrodes attached externally to the body are a major source of signal quality problems and analysis errors because of susceptibility to interference such as muscle noise, power line interference, high frequency communication equipment interference, and baseline shift from respiration. Signal degradation also occurs due to contact problems, ECG waveform artifacts, and patient discomfort. Externally attached electrodes are subject to motion artifacts from positional changes and the relative displacement between the skin and the electrodes. Furthermore, external electrodes require special skin preparation to ensure adequate electrical contact. Such preparation, along with positioning the electrode and attachment of the ECG lead to the electrode needlessly prolongs the pacemaker follow-up session. One possible approach is to equip the implanted pacemaker with the ability to detect cardiac signals and transform them into a tracing that is the same as or comparable to tracings obtainable via ECG leads attached to surface electrodes.
It is known in the art to monitor electrical activity of the human heart for diagnostic and related medical purposes. U.S. Pat. No. 4,023,565 issued to Ohlsson describes circuitry for recording ECG signals from multiple lead inputs. Similarly, U.S. Pat. No. 4,263,919 issued to Levin, U.S. Pat. No. 4,170,227 issued to Feldman, et al, and U.S. Pat. No. 4,593,702 issued to Kepski, et al, describe multiple electrode systems that combine surface EKG signals for artifact rejection.
The primary use for multiple electrode systems in the prior art appears to be vector cardiography from ECG signals taken from multiple chest and limb electrodes. This is a technique whereby the direction of depolarization of the heart is monitored, as well as the amplitude. U.S. Pat. No. 4,121,576 issued to Greensite discusses such a system.
Numerous body surface ECG monitoring electrode systems have been employed in the past in detecting the ECG and conducting vector cardiographic studies. For example, U.S. Pat. No. 4,082,086 issued to Page, et al., discloses a four electrode orthogonal array that may be applied to the patient""s skin both for convenience and to ensure the precise orientation of one electrode to the other. U.S. Pat. No. 3,983,867 issued to Case describes a vector cardiography system employing ECG electrodes disposed on the patient in normal locations and a hex axial reference system orthogonal display for displaying ECG signals of voltage versus time generated across sampled bipolar electrode pairs.
U.S. Pat. No. 4,310,000 to Lindemans and U.S. Pat. Nos. 4,729,376 and 4,674,508 to DeCote, incorporated herein by reference, disclose the use of a separate passive sensing reference electrode mounted on the pacemaker connector block or otherwise insulated from the pacemaker case in order to provide a sensing reference electrode that is not part of the stimulation reference electrode and thus does not have residual after-potentials at its surface following delivery of a stimulation pulse.
Moreover, in regard to subcutaneously implanted EGM electrodes, the aforementioned Lindemans U.S. Pat. No. 4,310,000 discloses one or more reference sensing electrode positioned on the surface of the pacemaker case as described above. U.S. Pat. No. 4,313,443 issued to Lund describes a subcutaneously implanted electrode or electrodes for use in monitoring the ECG.
U.S. Pat. No. 5,331,966 to Bennett, incorporated herein by reference, discloses a method and apparatus for providing an enhanced capability of detecting and gathering electrical cardiac signals via an array of relatively closely spaced subcutaneous electrodes (located on the body of an implanted device).
More recently, patent application Ser. No. 09/697,438, filed Oct. 26, 2000, entitled Surround Shroud Connector and Electrode Housings for a Subcutaneous Electrode Array and Leadless ECGs, by Ceballos, et al., incorporated herein by reference in its totality, discloses an alternate method and apparatus for detecting electrical cardiac signals via an array of subcutaneous electrodes located on a shroud circumferentially placed on the perimeter of an implanted pacemaker. An associated submission, patent application Ser. No. 09/703,152, filed Oct. 31, 2000, entitled Subcutaneous Electrode for Sensing Electrical Signals of the Heart by Brabec et al, incorporated herein by reference in its totality, discloses the use of a spiral electrode using in conjunction with the shroud described in patent application Ser. No. 09/697,438. In addition, patent application Ser. No. 09/696,365, filed Oct. 25, 2000, entitled Multilayer Ceramic Electrodes For Sensing Cardiac Depolarization Signals by Guck et al, also incorporated herein by reference in its totality, discloses the use of the aforementioned electrodes around the perimeter of an implanted pacemaker.
The present invention encompasses a Subcutaneous Thin Film Electrode that is applied to the uppermost surface of a feedthrough and placed into an assembly that is welded individually into three or four openings placed around the perimeter of an implantable pacemaker. These electrodes are electrically connected to the circuitry of a pacemaker to form a leadless Subcutaneous Electrode Array (SEA) for the purpose of detecting cardiac depolarization waveforms displayable as electrocardiographic tracings on a Programmer screen when the programming head is positioned above an implanted pacemaker (or other implanted device) so equipped with a leadless SEA.
This invention is designed to replace existing externally mounted electrodes and electrode wires currently used on the leadless ECG implantable pacemaker, as described in U.S. Pat. No. 5,331,966 issued to Bennett. This previous art had electrodes placed on the face of the implanted pacemaker. When facing muscle, the electrodes were apt to detect myopotentials and were susceptible to baseline drift. The present invention minimizes myopotentials and allows the device to be implanted on either side of the chest by providing maximum electrode separation and minimal signal variation due to various pacemaker orientations within the pocket because the electrodes are placed on the perimeter of the pacemaker in such a way as to maximize the distance between electrode pairs.
The invention will eliminate the need for a compliant shroud that houses surface mounted electrodes and connecting wires as described in patent application Ser. No. 09/697,438, filed Oct. 26, 2000, entitled Surround Shroud Connector And Electrode Housings For A Subcutaneous Electrode Array And Leadless ECGs, by Ceballos et al. The present invention will also eliminate the need for separate electrodes attached to a feedthrough with their associated assemblies such as those described in P-8786 Multilayer Ceramic Electrodes For Sensing Cardiac Depolarization Signals by Guck et al, and patent application Ser. No. 09/697,438, filed Oct. 26, 2000, entitled Subcutaneous Sensing Feedthrough/Electrode Assembly by Fraley, et al. Because the thin film electrode is applied to a feedthrough and is a complete functional component with its own hermetically attached weld ring, the assembly can be welded directly into the IPG casing. The use of this invention and the accompanying manufacturing process will eliminate the need for a compliant shroud as well as an attached, separately manufactured electrode. As a result, the manufacturing process will be easier to accomplish and be less expensive. In addition, the present invention provides improvements in the size and handling of the implantable pacemaker during the implant procedure.
The spacing of the electrodes in the present invention provides maximal electrode spacing and, at the same time, appropriate insulation from the pacemaker casing due to the insulative properties of the welding rings into which the electrodes are placed. The electrode spacing around the pacemaker""s perimeter maintains a maximum and equal distance between the electrode pairs, in either the three or four preferred electrode configuration as described in patent application Ser. No. 09/697,438.
As in the use of the compliant shroud disclosed in patent application Ser. No. 09/697,438 and helical electrode disclosed in patent application Ser. No. 09/703,152, the present invention also allows the physician or medical technician to perform leadless follow-up that, in turn, eliminates the time it takes to attach external leads to the patient. Such timesavings can reduce the cost of follow-up, as well as making it possible for the physician or medical technician to see more patients during each day. Though not limited to these, other uses include: Holter monitoring with event storage, arrhythmia detection and monitoring, capture detection, ischemia detection and monitoring (S-T elevation and suppression on the ECG), changes in QT interval, and transtelephonic monitoring.